Method of servicing wells



` T. o. ALLEN ET AL 2,842,205

METHOD oF sERvIcING WELLS July s, 1958 Filed Dec. 24, 1956 2 Sheets-Sheet l F'IG. 3.

F'IG. 2.

FIG. 1.

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m za @mm TL IN V EN TURS.

NN EA LO LL AS OM s Am MR OU HA TL T. o. ALLEN ET AL 2,842,205

METHOD 0F SERVICING WELLS July 8, 1958 Filed Deo. 24, i956 2 Sheets-Sheet 2 F' IG. 6.

FIG. 4.

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.il ru. 1 1 l f/L@2HE? FF p INVENToRs. THOMAS o. ALLEN BY LAURIE M. SLOAN,

ATTO NEY.

u .emulsion to produce a solids-free emulsion.

`reducing sugars.

State 2,842,205 METHOD or sani/remo WELLS Thomas 0. Allen, Bellaire, and Laurie M. Sloan, Houston,

1 Tex., assignors, by mesne assignments, to Esso Research ,and Engineering Company, Elizabeth, N. 3J., a corporation of Delaware f Application December V24, 195.6, Serial No. 630,327 v Y claims. (ci. 16s-21) `The present` invention is directed to-'a method for servicing a well.y More particularly, they invention is directed to amethod for sealing selectively a `channel in a well back of a Wellcasing.1 In` its more specific aspects the invention `is directed to closing roi a lchannel y in a Well back of a well casing which iiuidly communi' cates vertically spaced apart zones.

The present invention may -be ybrieliy describedras a method for sealing selectively a channel in a well back of a well ycasing in which the channel communicates uidly with vless thanall of a plurality of adjacent first procedure involved,l fluid communication is established characteristic of low filtration rate and further the characteristic of maintaining perforationsopen ,withouty darn-fl j 1 faging or injuring the permeability and porosity of thelf` formation or interval with whichthey come into Contact."

In short, the low fluid loss nonfplugging fluids suitable for use in the present invention have the characteristic oflow ltration rate and of resisting entrance of other iluids into perforations in an earth formation. In addition, these fluids, particularlythose described in the several applications, do not damage `a formation with which they come into contact. j t

When a well casing is cemented'in a Well bore, a cement slurry is displaced intomtheannular' space between the well casing and the borehole to lill this space `andto sealV the casing in the Well bore. However, frequently the Y cement'fails toseal completely the anular space and after vperfroration's in the well casing. In the particular sealing .l

the cement has set voids or channels may be left in the set cement which may permit the vertical movement of for-4 mation fluids in the well bore outside the well casing.

The,vertical movement of :fluidsin the well bore outside the well casing is quite deleterious and disadvantageous in 'that when the Welljcasing is, penetrated, communication` between the channels outside the casing and the well casing may be established which will allow undesirable uids from an interval 'or formation `other than that perforated` to flow into the well casing. Forexample, if the chan-l Ynel opens up' into .a water bearing sand, water iniiux into between the channel and less than all ofa pluralityof adjacent second perforations in the well casing vertically spaced apart'from the firstperforations.l A low tluid n.

loss Ynon-plugging fluid is forced through the channel jandfollowing the low fluid loss non-plugging uid a sealing material is also 'forced through the channel. The sealing material is maintained in the channel with .pressurefbeing applied thereto for a suflicient length of time to cause the sealing materialto form a lilter cake in and seal the channel. Thereafter, any excess sealing materiai .is removed from the well casing and production is then had from the desired set of perforations.

The low uid loss non-plugging fluid may suitably` be ya uid such as an emulsion of an oilyphas'e and a Water phase and the like. Suitable'materials have been amply described in Serial No. 567,604, now U. S. IPatent 2,805,722, tiled February 24, 1956, for Bryan E. Morgan and yGerald G. Priest. The iiuids described in Serial No.

567,604 are eminently suitable in the practice of the present invention and comprise a stable emulsion of an oily medium and an aqueous medium lwhich hasga controlla- Y' "i f ble density, the density of the emulsion being adjusted by dissolving a weighting agent in onepof the phases of the Other suitable non-plugging perforating lluids are described in pendl ing application Serial No. 630,266, filed December 24,y

1 956, for Gerald G. Priest, Bryan E. Morgan, and Bertie F."Birdwell, in which an emulsion of an oily phase and an aqueous phase isdenscribed and claimed, thefemulsion y inrSerial No. l630,266 being a stable emulsion employing i C an emulsifying agent a'wat'er-soluble salt ofpurified -lignin-sulfonic acidfor a water-solubley salt of lignin sulfonic Vacid containing a certain amount of ash and Other non-plugging uids suitable'in the" practice lof the' present invention are ydescribed in l' Serial No. 630,026, entitled Well Completion Fluids and vtiled December 24, 1956, forGerald G. Priest, Bryan-E. Morgan, Melba L.` Lytle, Bertie` F, ,BirdwelL and Joseph- A. Caldwell.v In Serial No. 630,026,ja heatstable, non` corrosive emulsion is described 'and claimed in which an emulsifyingagent is employed and innwhich .theoily phase 1 of the emulsion comprises a substantial amount of tetrachloroethylene,l with kone of the phasesv of yithe'ernulsion containing a corrosion inhibitor." These several perforat-v .of more desirable earth fluids.

the casing may be serious Vand interfere with production In the present invention a method is described for sealf plugging with mud of perforations made` inthe well casingthrough which productionV is to be had'on completion of the channel repair operation.

. In workoveroperationswhere s alt wateror other high 1 filtration rate uidsare employed as the'workover fluid, j the present invention oiers considerable advantages` by* avoiding the loss oflarge quantities of vvorlroveriluid'v into theV productive "formation Yin turn, this avoids'a serious loss of hydrostatic pressure ofthe Viiuid in the Well bore which otherwise might lpermit a Well blowout.

Furthermore, the' present ,invention reduces Well cleaning time required to restore production on completionv of a n Y job in that :a clean perforating uid and workoyer fluid Ain' therpresent procedure.,

is used. nAlso the usualserious reduction in permeability to hydrocarbons ofjthe formation in the vicinity of theA well completion interval isavoided since'the workover interval is not invaded by theworkover fluid employed Furthermore, fthe present invention will, in many cases, avoid thenecessity for reperforating therinterval to be produced followingthe'sealng of the vchannelfbaclcof 'p the well casing, inasmuch as .the perforations 4through ik d Y which cement has been circulated willrbe sealed sel'erc-v f tively and successfully with tllejcement, Whereas theperving'fluidsdescribed,in the yseveral applications have f the forations not in communication with' the channel will not-4 be sealed. fIn other words, the iiuid employedin the practice of the present invention allows sealing selectively'vv of 'perforations in communicationv with-the channel while i maintaining openthe perforations not-in communication y with the channel;

. d -In the present invention a low Vfiltration rate non-plug-g ging Workover uid allows fluid Vcommunieation'f'vvitll the n Y channel in the. cernentbackfoffthewell casingA until seal- ,y L

ing material, such as uidicementyis displaced into ,the i c f 2,842,205 Patented July 8,

E channel. Thus, the sealing material is directed selectively into the channel and the sealing material is pre vented from entering perforations not in communication with the channel. As pointed out supra, this is quite advantageous in many ways and offers numerous advantages over the prior art.

The sealing material employed inthe practice of the present invention may suitably be a cement off the modilied type, 2,582,459. The cement may suitably be an oil emulsion cement and may contain Bentonite, which is montmoril'lonite, and other modifying agents. The cement is suitably a cement which remains fluid a sufficient length of time to allow excess duid cement to be circulated ,from the casing. Such cement readily forms iilter cakes opposite permeable formations while the remaining amount of the cement remains fluid in the well casing and may be removed. There are many modied cements having a retarded set which may be'employed in the practice of the present invention, although the employment of the conventional Portland cement used in cementing Well casing is not to be excluded from the practice of the present invention.

Suitably other sealing material, such as phenol-forrnaldehyde resins and urea-formaldehyde resins may be used. ln a word, it is contemplated that plastic materials which vare thermo-setting may be employed as the sealing material.

lt is also contemplated that pressures may be used in the practice of the present invention to force the low fluid loss non-plugging lluid or liquid into the channels and also to force the sealing material into the channel after the fluid. This pressure may be applied through the tubing or on the casing-tubing Yannulus or on both the tubing and the casing-tubing annulus as may be desired. Application of pressure enhances the formation of filter cakes of cement to lill and seal the channel.

The invention will be further illustrated by reference to the drawing in which:

Figs. l to 3 illustrate a stepwise procedure for repairing mel back of a well casing; and

s. 4 to 6 also represent a stepwise procedure of a modified mode of repairing a channel back of a well casing.

Referring now to the drawing in which identical numerals will be employed to designate identical parts, numeral l1 designates a well bore drilled from the earths surface to penetrate a plurality of subsurface intervals, zones, horizons, strata, formations, sands, and the like, 12, i3, i4 and l5. The well bore il has a casing i6 arranged therein and cemented in place with cement i7.

The cementing operation in the present invention is faulty in that a channel such as i8 exists back of the casing 16 and extends from the formation or sand 1S to the formation or sand l2.

The casing i6 has been perforated in the interval l2 to form perforations 19 employing a perforator such as a bullet gun perforator, a shaped charge perforator, a chemical perforator or a mechanical perforator. Such perforator may be one that is run down the casing or one which may be sutliciently small in diameter to be run through the tubing set with its lower open end above the formation or sand to be perforated.

Referring to Fig. l, it will be seen that uid may pass from the formation l to communicate with the well casing 16 through the perforations 19. If the perforations 19 are producing excessive gas and it is desired to produce from interval i5 instead of interval 12, the channel i8 may prevent the exclusion of the fluids from lzwhen the usual recompletion techniques are employed. In the present invention the channel 18 may be repaired as shown in Fig. 2. In repairing the channel 1S, perforations 20 are formed in the interval 15. These perforations 20 may be formed by employing a perforator of the type illustrated before, which may be run through such as described in the Salathiel Patent the casing or through a tubing such as 2l which may be run into the casing with a packer Z2 to isolate the intervals 12 and l5, the tubing 2l being arranged with its lower open end 23 above the interval l5. Prior to forming the perforations 7.0, a body of non-plugging lluid, such as 24, is placed in the casing lr6 to cover the region in the casing adjacent the interval l5. Thereafter a gun perforator, such as 2', which may be, for purposes of illustration only, a shaped charge perforator, is lowered en a wire line 26 until it is opposite the interval l5, and tl e perfo-rater is then tired to form the perforations 20. Thereafter, pressure is imposed on the body 24 to cause a portion of the body to be forced through the channel ad to communicate with the perforations 19 in the al if. which communicate with the channel 18. The portion of the body of non-plugging fluid 2.4 which has entered the perfo-rations Ztl protects the perforations Zr which are not in communication with the channel 1.3. Thereafter, fluid cement may be forced down the tubing Zi to displace the body 24 and to cause the tluid cement to be forced up through the channel l as shown more clearly in Fig. 3, the gun perforator having been removed. The body of fluid cement is generally indicated by the numeral 27, Vwhile the non-plugging lluid which has entered the perforations Ztl protects the perforations 2S not in communication with the channel i8. Pressure is imposed on the cement body 27 and on the channel 18 for a sufficient length ol` time which may range from about 5 to 30 minutes to cause the cement to form a filter cake iilling the channel and become immobile there- Thereafter, the packer 22 is unseated and the tubing is lowered until its lower end is below the interval l5. The excess fluid cement 27 and the non-plugging fluid may then be circulated out of the well by reverse circulation down the annulus 3l and up the tubing 2l to the wellhead. After removal of the excess fluid cement and any excess non-plugging [luid the packer Z2 isreset above the interval l5. After allowing time for the cement in the channel and in the perforations .in communication with the channel to become set, production may be had from the perforatio-ns 2@ not sealed with cement by swabbing the well or by reducing thc pressure in the well by any well known means.

if a non-retrievable .packer is used as the packeriZZ instead of the retrievable tubing packer 22 contemplated in the detailed example just described, a tubing extension member 28 is lowered, before cementingthe channel,

on a wire line, not shown, through the tubing/2.1 andV supported in a landing nipple 29 which seals and supports the tubing extension 28 in the tubing 2l, theupper end of the tubing extension 23 being provided Vwith a hanger il for supporting same, the tubing extension member being open on both ends. ing means from the packer 22 after cement has-formed a iilter cake in the channel i8, the excess fluid cement 27' and the nonnplugging fluid may then be circulated out of the well by reverse circulation down the annulus 31 and up the tubular extension member 23 and then up the tubingl 2l to the Wellhead. After removal of the excess liuicl cement and any excess non-plugging liuid, the tubing sealing means is reset in the packer 22, and after waiting for the cement in the channel to become set, production may be had from the perforations 20 not sealed with cement by swabbing the well or by reducing the pressure inthe well by any well known means. The tubing extension member 2? may be left in place or may be removed as desired.

The tubing extension member 218 may also be used with a retrievable tubing packer 22 if desired. Its use eliminates the necessity for lowering the tubing 2l after cementing the channel, but instead of removing the tubing sealing means from the packer 22 as in the case of By removing the tubing seal-f the non-retrievable packer, the'retrevable packer 22 is .unseated to permit reverse circulation for removal of excess cement, vthen the retrievable packer is reset Vafter the'reverse circulation is completed and before production'of hydrocarbon fluids is initiated from the perforations 20 remaining open after the channel has been sealed.

lIt will, be noted that, inthi's mode of the present invention, the packer 22 isolates the formation 12 from` -fthe formation and the channel 18 is sealed allowing production to be had fromthev formation or interval 15. 7. l:While the intervals 12,13, 14, and 15 have been describedl as vbeing separate intervals or zones, it is to beclearly understood that this is by way of illustration i j andnot by way of limitation, in that the intervals 12,

13, 14 and 15, while vertically displaced from each other, maybe in the same sand, zone, horizon, strata, and thev like.

Referring now to Figs. 4 to "6another mode of pracvtice of the presentinvention willg'be described Where a channel, such as 18, exists back'of the wellvcasing 16 in the cement 1'7, as has been described with respect to Figs. l` to 3. In this particular instance, perforations such, as y26 have been formed.` in the interval 15, and sorneljofathese perforations communicate with the channel-"18 through which undesirable earth fluids such- 'as-@gas fare passing to be produced throughperforations 24Min communication with the channel. 'with this mode of our invention, a body such as .24a

vof 'non-plugging perforating uid of the type described y supra is arranged in the Well vcasing 16 in a suiicient.V amount. tomove the perforations 26 and to extend'in` In accordance the well upwardly a sucient distance to cover a level l in the casing adjacent the interval 12. After the non- Aplugging yperforating uid 24d. is placed. in the casing I16,.the casing v16 is then perforated in the :interva1'j12 Vtoform the perforations 19. This may suitably vbe done `by Vlowering a gun perforatonsuch as l through the f casing 16, if no tubing is arranged therein, or lowering afgun perforator lsuch as 25 which is 0fv a dimension i small enough to be lowered through atubingsuch as 21.k Assuming that the gun perforator is a casing gun perforator, the-perforations 19 are made in the casing 16, and thereafter the tubing 21 is run into theperforated casing with a packer 22 whichis set between the intervals 12 and 15. `The non-plugging perforating uid 24a isthen.- above and below the packer, and lby 'imposingy uid pressure through the tubing 21, ow of iluid `through thecasing-tubing annulus 31 at the wellhead will indicate perforating .after resetting the packer 22 between-,inter-ff vals 12 and 15.

f It is contemplatedin thepractice of the present inven-` v tion that rather than circulating out the cement, particu# 1 larly where a modified cement is not used, the cement may v be drilled out.

In o rder to describethe invention further, an'roperation was performed in a field in Texas inv a well which was producing oil withr a high gas-oil ratio. These operations were conducted in a procedure as outlined withrespect to Figs. 1 to 3. -It'was suspected ythat a channel v existed in the cement between two intervals, such as 12 Aand 15. A low fluid loss non-plugging fluid Vwas dis.-

placed .into the well oppositethe intervaLvsuch as 15, .and extending several feet'above thatinterval.- YT he cas ing was then perforated in the interval equivalent'to 15 and well tubing was run with a non-retrievable packer as illustrated. in Fig. 2. Fluid pressure was then applied below the packer to the equivalent of perforations 20. The fluid in the equivalent ofl channel 18 and the huid in the perforations .equivalent to 20 were.v displaced bythe pressured uidvthrough the channel and into the equivalent of the tubing-casing annulus 31 through the lequival' lent of perforations 19 communicating with the channel. The return of iluid to the surface in this particular Swell gave a positive indication of the presence of'achannel. A tubing extension member such as 28 was'installed by wire.` line in the tubing 21being seated therein by means of. a hanger such as 30 `and a landing nipple such as29. f

A modiied'cement slurry was circulated intothe channel vbypumping it down the tubing and displacing it with another fluid. Application of huid pressure less than the pressure 'required to` fracture the formation to the iiuids inthe tubing and tubing-casing annulus caused dehydration of the cementvin the channel r113l in communication with the permeable formations 12.and 15. Excess cementing material was then circulated from the well'after v removing the tubing sealing means from the nonfretriev l able'packer. kIn this particular operation, the tubing exthat a channel 18 exists back of the casing 16. However,` f the. non-plugging perforating uid 24a willl protect the perforations 19 and 20 not in communication with. the `rchannel l18. Thereafter, as described with respect to Figs.

. A1 vto 3,- a body of a tluid cementitious material suchfas.` a Portland cement slurry, which may be an oil-emulsion slurry, or a slurry of lthe `type described in the Salathielr Y patent supra, or a plastic material, is forced down the tubv` ing 21 and through the perforations 20 in communication Y with the channel 18 and into the perforations '19 in com-v munication with the channel 18, lling and sealing same with .pressure being imposed as'desired, eitheron the annulus 31, orthrough thetubing 21, or on'the annulus 31fand on'the tubing 21 to cause thecement to deposit 'a lter cakeflling' the channel `18.

l .v The body of cement and anynon-pluggingiiuid is then removed'A by unseating the .packer 22 and circulating the excess fluid cement by owing a fluid down throughthe annulus 31 up through the tubing extension 28 and yup the tubing V21. It will be seen that in these operations the perforations, 2t) not-in communication with the-'channel 18j and the perforations 19 not in commuication with the channel 1S havey been selectively protected against the cement and.y against any drilling mud. Fluid production may then be reestablished from interval 15 Without retension memberwas retrieved 4andiuid production was then initiated from ythe perforations equivalent v to 20 without' requiring reperforat'ing in the interval equivalent to l5, since the non-plugging fluid prevented the`cement v ing materialfromentering and 'sealing the perforations' 20 which were not Vin communication with, thechannel 1S. lThis operation kwas quite successfuland productionwas then had again withoutfreperforating. 'y

In anothermode lof operation similar to ythat of Fig.

l, salt water may be entering the welly through the cement channel from a level below theperforations such as 19.

The channel 1S ymay be sealed ina similar manner "to that e described, but in this particular instance, the nonplug ging uid may be employed in suflicient amount tocover the interval 12 and the interval 15 in-the well casing.

Also, after perforating to form the perforations 2h and employing cement `to seal the channel `18, cement :may be left inthe well bore extending to a level above the per'- forations 20. Production of reservoir fluids Vmay* then beresumed through the perforations 19 without reperforating the intervalv 12'. n In another operation whereexcessive amounts of salt water :are being produced from an interval `such as 15 as illustrated Vin Fig. 4, itrnay be desirable to Vrecomplete the Well through perforations such as 19 in `the in- In this instance, like in `the'other instances,

terval 12. n a channel such as 18 may exist between the two intervals which wouldpermit the continued'intrusion of watery from the interval 15. In this particular operation a low fluid loss non-plugging fluid is employed `in an amount sucient to lill the casing from the interval 15 extending through the interval 12, then the perforations 119 are placed 1in the interval 12.V As shown in lli'g. 5;'a

sealing means, such vas 22, which may *beV ay retrievable cementing .packer or a cementretainer, is set between the Vperforated"'intervals such as 12 and 15 "and tubing is connected to the sealing means as shown in Fig. 5. Fluid pressure is applied through the tubing to the interval below the cement retainer and causes movement of uids up through the channel 1S which is reected by llow of well tluids to the surface through the tubing-casing annulus 3l. Portland cement slurry or other sealing material, as illustrated, may be circulated down the tubing and out through the perforations 20 up the channel 18 and through the perforations 19 in the interval 12. 0f course, it is realized that the cement flows only through the perforations ll@ and 26 in communication with the channel 3.8. Fluid pressure is applied to the well bore through both the tubing and the tubing-casing annulus and causes dehydration of the cementitious material in the channel, sealing the channel. Excess cernentitious material is circulated from the well bore down to the cement retainer or other sealing means 22, or it may be drilled from the casing down to that depth after the cement has been set. The well is then produced through the perforations 19 not in communication with the channel i8, which has been sealed, the non-plugging iluid protecting the perforations 19 which are not in communication with the channel 18.

It will be seen from the foregoing description taken with the drawing and the several examples that a. new and useful and quite advantageous procedure has been described in which a channel is selectively sealed back of a well casing by Vemploying a non-plugging fluid which allows a sealing material to enter only perforations in communication with the channel while protecting the perforaticns not in communication with the channel. The present invention has been employed successfully in held operations and is of demonstrated commercial worth.

The nature and objects o the present invention having been completely described and illustrated, what We wish to claim as new and useful and secure by Letters Patent is:

l. A method for sealing a channel in a well back of a l well casing in which the' channel communicates luidly with vertically spaced apart zones and fluid from a first of said zones is invading a second of said zones and in which the channel also communicates fluidly with less than all of a plurality of rst perforations in said casing in said first zone which comprises establishing fluid communication between said channel and less than all of a plurality of second perforations in said casing in said second zone vertically spaced apart from the rst perforations, forcing a low liuid loss non-plugging fluid through said channel through said perforations in fluid communication with said channel, then forcing a sealing material through said channel after said fluid, and maintaining said sealing material in said channel and said perforations in fluid communication with said channel a suficient length of time for it to seal said channel and said perforations in communication with said channel, said low fluid loss non-plugging fluid having the characteristics of resisting entrance of other fluids into the perfcrations other than the perforations in fluid communication with the channel.

2. A method in accordance with claim l in which the casing is isolated between the rst and vsecond perforations and in which production of well uids is initiated through one or" the plurality of irst and second perforations other than the sealed periorations after sealing the channel. y

3. A method for sealing a channel in a well back of a well casing in which the channel communicates iluidly with vertically spaced apart zones and uid from a iirst of said zones is invading a second of said zones and in which thc channel also communicates iluidly with less than all of a plurality of rst perforations in said casing in said rst Zone which comprises placing a body of a low liuid loss non-plugging lluid in said well casing at a level adjacent said second zone and vertically removed Eil from the first perforations, perforating the well casing in `said body to form a plurality of second perforations in said casing in -said second Zone and thereby establishing iluid communication between said channel and less than all of said plurality of second perforations, forcing at least a portion of said body through said channel from said first perforations to said second perforations in iluid communication with said channel, then forcing a sealing material through said channel after said body, and maintaining said sealing material in said channel and said perforations in lluid communication with said channel a suliicient length of time for it to set and seal said channel perforations in fluid communication with said channel, said low fluid loss non-plugging fluid having the characteristics of resisting entrance of other iluids into the perforations other than the perforations in fluid communication with the channel.

4. A method in accordance with claim 3 in which the casing between the iirst perforations and the level where the body is placed is isolated prior to perforating the casing in said body and in which production of well lluids is initiated through the second perforations after sealing the channel.

5. A method for sealing a channel in a well back of a well casing in which the channel communicates fluidly with vertically spaced apart zones and iluid from a first of said zones is invading a second of said zones and in which the channel also communicates fluidly with less than all of a plurality of rst perforations in said casing in said first zone which comprises placing a body of a low fluid loss non-plugging duid in said well casing adjacent said plurality of rst perforations, establishing uid communication between said channel and less than all of a plurality of second perforations in said casing adjacent said second zone and vertically spaced apart from the tirst perorations, forcing at least a portion of said body through said channel from the lirst perforations in lluid communication with said channel to the second perforations in luid communication with said channel, then forcing a sealing material through said channel after said body, andmaintaining said sealing materialn said channel a sufficient 'length of time for it to seal said channel and perforations in duid communication with said channel, said low fluid loss non-plugging fluid having the characteristics of resisting entrance of other fluids into the perforations other than the perforations in fluid communication with the channel.

6. A method in accordance with claim 5 in which the sealing material is uid cement.

7. A method in .accordance with claim 5 in which the sealing material is a plastic.

8. A method in accordance with claim 5 in which the non-plugging fluid is a stable emulsion of an oily phase and an aqueous phase.

9. A method for sealing a channel in a well back of a well casing in which the channel communicates fluidly withV vertically spaced apart zones and fluid from a first of said Zones is invading a second of said zones and in which the channel ralso communicates fiuidly with less than all of a plurality of lirst perforations in said casing in said'tirst zone which comprises placing a low fluid loss non-plugging tluid in said Well casing adjacent said plurality of rst perforations, establishing fluid communication between said channel. and less than all of a plurality of second perforations in said casing adjacent said second zone and vertically spaced apart from the rst perforations, applying pressure to said body to force at least a portion of said body through said channel from the lirst perforations in lluid communication with said channel to the second perforations in luid communication with said channel, placing a sealing material in said well casing adjacent said plurality of first perforations, then forcing said sealing material through said channel after said body, and maintaining said sealing material in said channel a sufficient length of time for it to seal said channel and perforations uid communication with said channel, said low kfluid `loss non-pluggingfluid having the characteristics of resisting entrance n of other liuids into the perforations4 other than the perforations in fluid communication with the channel.

10. A method for sealing a channel in a well back'of a wellcasing in which the channel communicatesuidly K withy vertically spaced apart zones and lluid from a first of said zones is invading a second of said zones and in which the channel also'communicates fluidly with less and less than all of said plurality of second perforations,

forcing at least` a portion of said 'liuid'ltlirough' said channel from lthelirst to the second perforations in fluid v communication with said channel, then forcing a sealing material through said channel after said uid, and maintaining said sealing material in ysaid channel and perforations in fluid communication with said channel a sutiicient length of time for itl to form a lilterfcake in of a plurality of second perforationsfin saidr casing i said `second zone vertically spaced apart from the Vfirst perforations, forcing a 10W rfluid loss non-plugging-'luid through said channel 'from one to the otherofthe*perforations in fluid communication with said channel, then forcinga sealing material through said channel after f i said iluid, maintaining said sealing material in said chan- Y nel and said perforations in liuidcommunicationlwith said channel a suflicientlengthV of time for, itfto seal said channel and said perforations in liuid communicationy L' f with( ,said channel, said low fluid loss non-plugging fluid and seal said channel andeperforations in fluid communication with said channel, said low fluid loss nonplugging kfluid having the characteristics of resisting entrance of other fluids into the perforations other than the perforations in fluid communication with the channel.

ll. A method in accordance with claim l0 in which the well is provided with a tubing and in which the casing is isolated aty 4a level between the perforations and pressure is applied on said fluid and on said sealing material through the tubing.

l2. A method in accordance with claim 1l in which pressure is also applied in the vannulus between the tubing :andr casing on the fiuid and rsealing material. a

13. A method for `sealing va channel in a well back of a well casing in. which the channel communicates lluidly with vertically spaced apart zones and fluid from a first of said zones is invading a second of said zones and in which the channel also communicates lluidly with less than all of a plurality yof first perforations in said casing in said first zone which comprises establishing uid communication between said channel andv less than all having the characteristics of resisting entrance OfOther i fluids into vthel perforations other than the perforations in liuid communication with thechannel, and then producing well fluids through oneof the plurality of rst and second perforations other than the sealed perforations.

14. A method for sealing a channel in a well back of a well casing'in which the channel communicates fluidly with vertically spaced apart zones land fluid from av irst: n of said zones is Vinvading :a second 'ofsaid zvonesvand inv which the channel alsok communicatesfluidlywith less than all of a plurality of firstlperforations in'- s'aid casing in said first zone which comprises establishing uid com munication between said channel and lessrgthan all of ai a i plurality of second perforations in'said casing in said second zone vertically spaced apart from theV first per-k forations, forcing a. low fluid loss non-plugging liuid through said channel from one to the other of the perforations in fluid communication with said channel, v1

then forcing a sealing material through said channel after said iluid, maintaining said sealing material in said channel and said perforations in liuidcommunication with said channel a sucientlength of'tirne for it toform a filter cake in and seal said channel and said .perforations in fluid communication with'said channel, andremoving any excess sealing material' from ,the casing, said low fluid loss nonplugging fluid having the characteristics of resisting entrance of other fluids into the perforationsy other than the perforations in uid communicationwith the channel. i

15. A method vin accordance with claim 14 in which the sealing material is fluid cement and the excess is moved by circulation. l ReferencesCited in the file of this patent UNITED STATES PATENTS 2,223,397V white et al. Dec. 3, '1940 2,718,264'` Amener-a1. -s,epr=.`2o,.1955 

1. A METHOD FOR SEALING A CHANNEL IN A WELL BACK OF A WELL CASING IN WHICH THE CHANNEL COMMUNICATED FLUIDLY WITH VERTICALLY SPACED APART ZONES AND FLUID FROM A FIRST OF SAID ZONES IS INVADING A SECOND OF SAID ZONES AND IN WHICH THE CHANNEL ALSO COMMUNICATESZ FLUIDLY WITH LESS THAN ALL OF THE PLURALITY OF FIRST PERFORATIOPNS IN SAID CASING IN SAID FIRST ZONE WHICH COMPRISES ESTABLISHING FLUID COMMUNICATION BETWEEN SAID CHANNEL AND LESS THAN ALL OF A PLURALITY OF SECOND PERFORATIONS IN SAID CASING IN SAID SECOND ZONE VERTICALLY SPACED APART FROM THE FIRST PERFORATIONS, FORCING A LOW FLUID LOSS NON-PLUGGING FLUID THROUGH SAID CHANNEL THROUGH SAID PERFORATIONS IN FLUID COMMUNICATION WITH SAID CHANNEL, THEN FORCING A SEALING MATERIAL THROUGH SAID CHANNEL AFTER SAID FLUID, AND MAINTAINING SAID SEALING MATERIAL IN SAID CHANNEL AND SAID PERFORATIONS IN FLUID COMMUNICATION WITH SAID CHANNEL A SUFFICIENT LENGTH OF TIME FOR IT TO SEAL SAID CHANNEL AND SAID PERFORATIONS IN COMMUNICATION WITH SAID CHANNEL, SAID LOW FLUID LOSS NON-PLUGGING FLUID HAVING THE CHARACTERISTICS OF RESISTING ENTRANCE OF OTHER FLUIDS INTO THE PERFORATIONS OTHER THAN THE PERFORATIONS IN FLUID COMMUNICATION WITH THE CHANNEL. 